II. Vulnerability information

III. Overview

WordPress platforms use a parameter called ‘author’. This parameter accepts integer values and represents the ‘User ID’ of users in the web site. For example: http://www.example.com/?author=1
The problems found are:

User ID values are generated consecutively.

When a valid User ID is found, WordPress redirects to a web page with the name of the author.

These problems trigger the following attack vectors:

The query response discloses whether the User ID is enabled.

The query response leaks (by redirection) the User Name corresponding with that User ID. (See update for version 3.1.3)

User IDs can be disabled, leaving holes within the consecutive numbers. Therefore, when an invalid User ID is sent, no redirection is done and no information is disclosed.

Also, the attack can be automated, sending multiple queries to extract valid User Names and User IDs from the vulnerable web sites.

Update:

In version 3.1.3 the redirection explained in the second attack vector is not done, but is still possible to find the User Name in the source code. Therefore, this version is still vulnerable.

IV. Affected versions

This issue was tested in versions 2.6, 3.1, 3.1.1, 3.1.3 and 3.2-beta2. Other versions were not tested and may be vulnerable.

V. Non affected versions

VI. Proof of concept

VII. Solution

WordPress version 3.1.3 fixes the redirection problem, but user names are still been disclosed in the HTML code. No solution was provided for this last problem.

VIII. Disclosure timeline

2011-03-14:

Vulnerability was identified.

2011-05-11:

WordPress security team was contacted.

2011-05-12:

WordPress confirmed the vulnerability.

2011-05-25:

WordPress released version 3.1.3, which included a fix for canonical redirection problem but did not included a fix for the source code problem.

WordPress security team was informed that after the release of version 3.1.3 the vulnerability was still exploitable.

WordPress team agreed to release the security advisory.

2011-05-26:

The advisory was released.

IX. Credits

This vulnerability was discovered and reported by Verónica Valeros (veronicavaleros at talsoft.com.ar)

X. Disclaimer

The information provided in this document is for information purposes only. Talsoft S.R.L. accepts no responsibility for any damage caused by the use or misuse of this information. The content of this advisory may be distributed freely, provided that no fee is charged for this distribution and proper credit is given.

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Talsoft S.R.L. is also involved in many information security research projects.